1. Field of the Invention
The present invention relates to process for preparing trichlorosilane, and, more particularly, to a process of preparing trichlorosilane, in part, by lamination.
2. Description of the Related Art
The present invention relates to the field of preparing high purity trichlorosilane (abbreviated as TCS) from mixed silane stock.
TCS is a valuable intermediate product used to produce various silanes for electronics and adhesives. TCS, especially the high purity grade, is used in the electronics industry including use in the preparation of solar and electronics grade polycrystalline silicon, which produces silicon tetrachloride as a by-product.
The general process of preparing high purity TCS from silicon and hydrogen chloride, or from silicon tetrachloride and hydrogen in the presence of silicon and hydrogen chloride at relatively low temperatures is known from many patents, including, for example, U.S. Pat. Nos. 4,117,094 and 4,424,198 as well as CA A-1,162,028.
The use of alkaline salts as an aid to the selectivity of the reaction toward TCS is known, for example, from U.S. Pat. No. 5,871,705. Powdered copper catalysts have been used in this industry for this reaction for some time. The use of powdered copper or mixtures of copper metal, metal halides and bromides or iodides of iron, aluminum or vanadium is reported to react silicon with silicon tetrachloride, hydrogen and, if necessary, hydrogen chloride. See, for example, Chemical Abstracts CA 101, no. 9576d, 1984 and Chemical Abstracts CA 109, no. 57621b, 1988.
Copper oxide catalysts have been noted to be ground to particle sizes below 0.01 mm to improve reaction rates by providing as homogeneous distribution of catalyst on the silicon as possible. It has also been noted that potentially more effective catalysts such as, for example, metal chlorides, are generally not used because of the lack of availability in the required fineness of the associated particles.
As is known from, for example, DE 41 04 422 A1, silicon may be reacted with hydrogen chloride, or silicon tetrachloride may be reacted with hydrogen in a fluidized bed without using pressure in the presence of copper salts of a low, aliphatic, saturated dicarbon acid, particularly copper oxalate.
It is known to those of ordinary skill in the art that trichlorosilane is usually produced in a fluidized bed. There is a disadvantage to using such a fluidized bed with copper catalysts and/or catalyst mixtures containing copper because very often small catalyst particles are carried out of the fluidized bed. This results in a significant decrease in the yield of the desired trichlorosilane in the course of the process, and new and/or additional catalyst must be introduced. Losing catalyst in this fashion causes additional economic costs, particularly when copper catalyst is used, since copper catalyst is comparatively expensive.
What is needed in the art is a method for producing trichlorosilane that is characterized by a high reaction velocity and a high space-time yield respectively.